U.S. Pat. Nos. 3,288,142 and 3,527,226 to Hakim relate to catheter systems for relieving pressure build up within the brain. These patents disclose systems that continuously control drainage of cerebrospinal fluid from the brain and release that fluid into the body. As seen most clearly in FIGS. 1 and 3 of the '226 patent to Hakim, one process for draining fluid away from the brain utilizes a valve unit having entrance and exit valves respectively. This allows the valve unit to be used as a pump to help unclog a blocked drainage catheter.
Both valves within the valve unit of the '226 patent are the same. They utilize a corrugated or convoluted spring element for biasing a trapped ball against a fluid inlet seat of the valve. Experience with the valve units shown in the '226 patent indicate the pressure at which fluid exits the brain using such a valve may be difficult to control.
Each pressure relief system must be evaluated prior to implantation within the subject since different pressures are chosen for different subjects depending upon the needs of that individual. If the valve pressure varies from its rated value, fluid pressures may rise or fall to dangerous levels.
Valve systems for ventricular shunting are discussed in a prior art publication entitled "Cordis Integral Shunt System", Copyright June, 1987. This publication is incorporated herein by reference. In this publication, the valve unit discussed in the '226 prior art patent noted above is characterized as a standard Hakim mechanism. A second unit characterized as a pediatric Hakim mechanism is also disclosed in the Cordis publication. This unit also includes two valves mounted within a valve housing for controlling pressure of fluid routed away from the brain to a drainage site. The two valves in the pediatric unit result in more uniform regulation of the fluid pressure passing through the unit.
Both valves in the pediatric Hakim mechanism include a coiled spring trapped between a valve body and a ball which selectively opens and closes against a valve body seat. The pediatric valve mechanisms are adjustable and experience with the pediatric unit suggests more accurate fluid pressure control is possible. A disadvantage, however, has been noticed with functioning of the pediatric unit depicted in the Cordis publication. High concentrations of protein may be suspended within the fluid routed away from the brain. This protein can clog the passageways in the valve unit resulting in an unstable operation. If the clogged portion is at the exit side of the valve unit, pumping action may successfully unblock the valve. If, however, the clogging occurs on the inlet valve, the blockage is not so easily opened.